Colony-stimulating factors (CSFs) are required for the growth and maturation of normal myeloid precursor cells in vitro, and a body of indirect evidence suggests that they are primary regulators of granulopoiesis in man. Human colony-stimulating factors have been difficult to characterize because until recently, only small amounts of partially purified protein were available. Our laboratory has recently purified a 22,000 MW human GM-CSF (granulocyte-macrophage colony-stimulating factor) that stimulates proliferation of hematopoietic progenitor cells and primes neutrophils for enhanced responsiveness to physiologic stimuli. Having obtained both cDNA and genomic clones encoding this human GM-CSF, it will now be possible to define the molecular mechanisms regulating its gene expression. GM-CSF mRNA has been detected in activated T lymphocytes and HTLV-infected T-lymophoblast cell lines, but not in resting T cells. The first steps will be to look for other sources of GM-CSF mRNA and to fully characterize the induction of GM-CSF mRNA expression seen with T cell activation. Next, the regions of the GM-CSF gene required for gene expression in activated T cells will be defined by making recombinant constructions containing fragments of the genomic GM-CSF clone linked to an enzyme marker and measuring gene expression. The precise DNA sequences necessary for regulation of GM-CSF gene expression will be identified by making a series of deletion mutants and by performing oligonucleotide-directed site-specific mutagenesis. I will also examine the role of trans-acting transcriptional activators on GM-CSF expression in both HTLV-infected T cells and activated T cells. These investigations should provide fundamental information regarding the expression of human cellular genes in physiologic and pathologic states. They should also provide valuable insights into the regulation of hematopoiesis and the process of neoplastic transformation.